Switching converter topologies are widely used as the major building block in high efficiency and lightweight power supplies such as those used in computer applications. A major shortcoming of switching converters, however, is its transient output response to a fast load change. Because most switching power converters include an output inductor, a switching power converter's transient response is inherently limited. For example, a typical buck converter comprises a power stage having a plurality of switches and an inductor-capacitor filter, and a feedback circuit. The feedback circuit monitors the converter output voltage and exerts pulse width modulation control over the switches. When there is a fast dynamic load change, the converter's ability to respond is limited by the feedback circuit and the power stage. The feedback circuits can be designed to respond quicker through traditional linear or non-linear approaches. The inherent response of the converter, however, is limited by the power stage and, in particular, the output inductor.
Some have attempted to improve upon the power converter's dynamic response by using an inductor with a small inductance value. This technique does improve the power converter's dynamic response because current flow can change much more quickly when a small indicator is used. This technique, however, is disadvantaged in that the use of a small inductor results in a ripple current during normal operation. High ripple current introduces high root mean square current in the converter switches and passive components and, as a result, increases the power loss.
Others have attempted to reduce power losses by using parallel switches to share the current, but this method increases the cost and complexity of the converters. Still others have attempted to improve upon the converter's transient response by increasing the converter's switching frequency. This technique is disadvantaged in that it induces excessive switching losses in the switches and excessive magnetic losses in the inductor core. Moreover, high frequency operation requires the use of high performance drive circuit which can further escalate the converter's cost.
Therefore, there remains a need for a method of providing a switching power converter with a fast transient response while minimizing the converter's power loss.